1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member and an electrophotographic apparatus using the electrophotographic photosensitive member.
2. Description of the Prior Art
As photoconductive material of an electrophotographic photosensitive member, inorganic photoconductive material exemplified by selenium, cadmium sulfide and zinc sulfide has been used. On the other hand, organic photoconductive material (OPC) exemplified by polyvinyl carbazole, oxadiazole and phthalocyanine has advantages in pollution-free characteristics and excellent producibility as compared with the inorganic photoconductive material. However, OPC suffers from unsatisfactory sensitivity.
The electrophotographic photosensitive member, of course, must have a predetermined sensitivity, electric characteristics and optical characteristics to be adaptable to an electrophotographic process to which it is applied. In particular, a photosensitive member, which can be used repeatedly, must have durability against electrical and mechanical forces, such as corona charge, toner development, transference onto paper and a cleaning process which is applied to the surface thereof. Specifically, the photosensitive member must have durability against deterioration in its sensitivity and potential and increases in its residual potential due to degradation which occurs due to ozone generated at the time of corona charging, wear and/or damage of the surface due to sliding and abrasion.
Since the surface of the photosensitive member is formed with resin, the characteristic of the resin is an important factor. Therefore, resins exhibiting excellent durability have been desired. Recently, polycarbonate (hereinafter called "bisphenol A-type polycarbonate") containing bisphenol A as the skeleton thereof has been investigated as a resin capable of satisfying the foregoing desire to serve as a binder for a surface layer. However, the bisphenol A-type polycarbonate cannot satisfy all required electrophotographic characteristics, resulting in the following problems which remain unresolved:
(1) Bisphenol A-type polycarbonate has satisfactory solubility with respect to only a portion of aliphatic hydrocarbon halides, such as dichloromethane or 1,2-dichloroethane. Since each of the foregoing aliphatic hydrocarbon halides has a low boiling point, a photosensitive member manufactured by using a coating liquid prepared by blending with the foregoing solvent allows the coated surface to be easily brushed. Moreover, it requires a long time to apply the coating liquid. PA1 (2) Even if the problem described in (1) can be improved, the polycarbonate, the main skeleton of which is only the bisphenol A derivative, encounters the problem of generation of solvent cracks. The foregoing problem causes cracks to occur in the surface of the photosensitive member in an electrophotographic copying machine.
Another attempt has been made wherein a substance of a type imparting lubricity is added to the photosensitive layer of the photosensitive member. Such a substance is exemplified by a leveling agent, silicone oil and the like. However, conventional surface property modifying agents suffer from unsatisfactory compatibility with the coating liquid on the photosensitive layer. That incompatibility causes a problem of unsatisfactory effect continuity because the modifying agent is shifted or oozed out onto the surface layer during long term use. What is worse, the surface property modifying agent is liable to readily trap carriers generated due to light, thus causing the residual charge to be increased after the electrophotographic process has been repeated.
Although Teflon powder or the like is sometimes dispersed in the photosensitive layer, the photosensitive layer in which the Teflon powder is dispersed exhibits the problem of unsatisfactory dispersion characteristics, deterioration in its transparency and trapping carriers.